Interconnections for plural and hierarchical p1500 test wrappers

ABSTRACT

A test architecture accesses IP core test wrappers within an IC using a Link Instruction Register (LIR). An IEEE P1500 standard is in development for providing test access to these individual cores via a test structure called a wrapper. The wrapper resides at the boundary of the core and provides a way to test the core and the interconnections between cores.—The test architecture enables each of the plural wrappers in the IC, including wrappers in cores embedded within other cores, with separate enable signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of prior application Ser. No.13/909,416, filed Jun. 4, 2013, currently pending;

Which was a divisional of application Ser. No. 13/892,473, filed May 13,2013, now U.S. Pat. No. 8,667,351, granted Mar. 4, 2014;

Which was a divisional of application Ser. No. 13/590,380, filed Aug.21, 2012, now U.S. Pat. No. 8,464,112, granted Jun. 11, 2013;

Which was a divisional of application Ser. No. 13/234,217, filed Sep.16, 2011, now U.S. Pat. No. 8,271,839, granted Sep. 18, 2012;

Which was a divisional of application Ser. No. . 13/028,606, filed Feb.16, 2011, now U.S. Pat. No. 8,051,349, granted Nov. 1, 2011;

Which was a divisional of prior application Ser. No. 12/887,664, filedSep. 22, 2010, now U.S. Pat. No. 7,913,135, granted Mar. 22, 2011;

Which was a divisional of prior application Ser. No. 12/403,791, filedMar. 13, 2009, now U.S. Pat. No. 7,831,875, granted Nov. 9, 2010;

Which was a divisional of prior application Ser. No. 11/759,025, filedJun. 6, 2007, now U.S. Pat. No. 7,525,305, granted Apr. 28, 2009;

Which was a divisional of prior application Ser. No. 11/096,399, filedApr. 1, 2005, now U.S. Pat. No. 7,242,211, granted Jul. 10, 2007;

Which was a divisional of prior application Ser. No. 10/028,326, filedDec. 21, 2001, now U.S. Pat. No. 6,877,122, granted Apr. 5, 2005;

which claims priority under 35 USC 119(e)(1) of Provisional ApplicationNo. 60/257,790, filed Dec. 22, 2000.

This patent is related to and incorporates by reference patentapplication Ser. No. 09/864,509 filed May 24, 2001, titled: 1149.1 TapLinking Modules.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

This Disclosure relates generally to testing intellectual property (IP)cores via a test structure called a wrapper. The wrapper resides at theboundary of a core and provides a way to test the core andinterconnections between the cores. Particularly, the Disclosure relatesto a test architecture for accessing wrappers within an integratedcircuit.

2. Description of Related Art

FIG. 1 illustrates the test structure of a prior art wrapper 100. Thewrapper includes test interface signals 109, an instruction register105, and set of data registers 106-108. The instruction register is aregister accessed by the test interface signals to load testinstructions that control the operation of the wrapper, in particularthe instructions control the selection of a data register and controlthe mode of operation of the selected data register. The selected dataregister may be accessed by the test interface to shift test data in andout of the wrapper. The set of data registers shown in FIG. 1 includes;(1) an internal scan register 108 for testing the core circuitry, (2) aboundary scan register 107 for controlling the inputs and outputs of thecore during testing, and (3) a bypass register 106 for bypassing thewrapper via a single bit. Any number of additional user defined dataregisters may be included in the set of data registers of the wrapper,such as data registers supporting core emulation and programmingoperations as described in the referenced patent application Ser. No.09/864,509.

The test interface 109 includes; (1) a clock signal for timing wrappershift and test operations, (2) a shift signal for enabling data to beshifted through the wrapper from the serial input (SI) to the serialoutput (SO), (3) a capture signal for causing data to be captured intothe instruction register or a selected data register, (4) an updatesignal for causing data to be output from the instruction register or aselected data register, (5) a reset signal for initializing thewrapper's instruction and data registers, and (6) a select signal forselecting data to be shifted through either the instruction registerfrom SI to SO, or through a selected data register from SI to SO.

In the example of FIG. 1, the test interface signals are simply gated,via AND gates (A), by the select signal to either allow them to becoupled to the instruction register or to the data registers. Othercoupling methods may be used, but gating is used in this example. As canbe seen, when select is high, gates 101 couple the test interfacesignals to the instruction register and the serial output of theinstruction register is coupled to SO via multiplexer 103. In thisconfiguration, the instruction register may be shifted via SI and SO forinstruction loading/unloading. When select is low, gates 102 couple thetest interface signals to the data registers and the serial output ofthe selected data register, as determined by the instruction loaded inthe instruction register, is coupled to SO via multiplexers 104 and 103.In this configuration, the selected data register may be shifted via SIand SO for data loading/unloading.

As one skilled in the art of testing will see, the IEEE P1500 wrapperarchitecture is similar to the IEEE 1149.1 boundary scan architecture.The main difference between the P1500 wrapper architecture and 1149.1boundary scan architecture is that the P1500 wrapper architectureaccesses the instruction and data registers using discrete testinterface signals 109 rather than accessing the instruction and dataregisters using the 1149.1's test access port (TAP) state machineinterface. Thus P1500 wrappers are free of 1149.1 TAP interfaces.

FIG. 2 illustrates a core 201 equipped with the wrapper 100 of FIG. 1.The test interface signals 109 of FIG. 2 are indicated as Control (CTL),and SI and SO are indicated as labeled in FIG. 1. As the name impliesthe wrapper simply wraps around the core to provide a test accessmechanism local to the core's input/output boundary. The instructionregister 105, bypass register 106, and boundary register 107 are part ofthe wrapper. The internal scan register 108 is part of the corecircuitry that may be accessed via the wrapper for testing the core.

FIG. 3 illustrates a prior art method of connecting three individualwrappers 307-309 of cores 1-3 onto a single scan chain arrangement 301.The wrapper arrangement 301 will exist inside an IC. The serial inputsof the wrappers 307-309 are indicated as SI-1, SI-2, SI-3. The serialoutputs of the wrappers 307-309 are indicated as SO-1-, SO-2, and SO-3.The test interface signals 109 are bussed to the CTL-1, CTL-2, and CTL-3inputs of wrappers 307-309.

As seen in FIG. 3, the arrangement 301 scan chain passes seriallythrough the wrappers 307-309 from SI 302 to SO 303. In this arrangement,all wrappers 307-309 can be controlled to load instructions via the SI302 and SO 303 scan path, or all wrappers 307-309 can be controlled toload data via the SI 302 and SO 303 scan path. Access to the SI 302, SO303, and test interface signals 109 of the arrangement 301 is typicallyprovided to tester external of the IC.

FIG. 4 illustrates the wrapper design of FIG. 1 being modified toinclude an enable/disable capability. The modification includes addingan enable signal 402 and adding circuitry 401 (i.e. the OR (O) gate, AND(A) gate, and an inverter), responsive to the enable signal 402 to causethe wrapper to either be enabled to respond to the test interface 109 orbe disabled from responding to the test interface 109. In this example,a low on enable 402 will disable the wrapper from responding to the testinterface 109 and a high on enable 402 will enable the wrapper torespond to the test interface 109.

FIG. 5 illustrates an alternate method of enabling/disabling wrappers.In this example, it is assumed the wrapper design is fixed (hard) andcannot be modified, as could the wrapper design of FIG. 4. With a fixedwrapper design, the enabling/disabling capability must be external ofthe wrapper. In FIG. 5, gating circuitry 501 is inserted into the testinterface 109 signal path to the wrapper and an enable signal 502 isadded and connected to the gating circuitry to either enable the testinterface signals 109 to be input to the wrapper or disable the testinterface signals 109 from being input to the wrapper. In this example,a low on enable 502 will disable the wrapper from receiving the testinterface signals and a high on enable 502 will enable the wrapper toreceive the test interface signals. The use of wrapper enable signals,while not necessarily as shown in the examples of FIGS. 4 and 5, isknown.

The IEEE P1500 standard will define the connections to a wrapper teststructure for an individual core of an IC. The standard leaves open theinterconnection of the wrappers around multiple cores and theinterconnection of wrappers around hierarchically arranged cores withincores.

SUMMARY OF THE DISCLOSURE

In accordance with the disclosure, the serial data paths into and out ofthe IC and into and out of the wrappers are selectively connectedthrough input linking circuitry and output linking circuitry. The inputlinking circuitry and output linking circuitry provide for selectiveserial connection of any one, plural, or all of the wrappers on the ICbetween the serial data input and serial data output.

In a hierarchical arrangement of cores and their wrappers, the input andoutput linking circuitry provide for selective connection of thehighest-level wrapper to be included in the selective serial connection.Additionally, the input and output linking circuitry provide for theselective connection of any one, plural or all of the lower levelwrappers to be included in the serial connection.

The disclosed circuits provide for the selective connection of thewrappers through use of control signals output from link instructionregisters. The link instruction registers produce these control outputsignals in response to instructions that are shifted into the linkinstruction registers. The link instruction registers also include abypass path so they do not affect the shifting of test data through theserial connection of the wrappers.

In a hierarchical arrangement of wrappers on an IC, a single enablesignal line may be available external of the IC for controlling theselective connection of the wrappers with a minimum number of controllines.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a known core test wrapper.

FIG. 2 illustrates a core with a known wrapper.

FIG. 3 illustrates a serial connection of three known wrappers.

FIG. 4 illustrates a wrapper with an internal enable circuit.

FIG. 5 illustrates a wrapper with an external enable circuit.

FIG. 6A illustrates a test architecture according to the Disclosure

FIG. 6B illustrates input linking circuitry of the FIG. 6A testarchitecture.

FIG. 6C illustrates output linking circuitry of the FIG. 6A testarchitecture.

FIG. 7 illustrates wrapper arrangements for the FIG. 6A testarchitecture.

FIG. 8A illustrates the FIG. 6A test architecture coupled to a LinkInstruction Register (LIR) according to the Disclosure.

FIG. 8B illustrates a 3-bit Instruction Register of the LIR.

FIG. 9 illustrates wrapper and LIR arrangements for the FIG. 8A testarchitecture.

FIG. 10 illustrates a wrapped core containing wrapped cores A and B.

FIG. 11 illustrates a test architecture for the wrappers of FIG. 10.

FIG. 12 illustrates FIG. 10 wrapper arrangements.

FIG. 13 illustrates a test architecture embedded within another testarchitecture.

FIG. 14 illustrates the hierarchical access of FIG. 13 wrapperarrangements.

FIG. 15 illustrates a test architecture including a LIR according to theDisclosure.

FIG. 16 illustrates a test architecture containing the FIG. 15 testarchitecture.

FIG. 17 illustrates the hierarchical access of FIG. 16 wrapperarrangements.

FIG. 18 illustrates further embedding of test architectures according tothe Disclosure.

FIG. 19 illustrates an alternate LIR circuit example.

FIG. 20 illustrates a serial connection of test architectures accordingto the Disclosure.

FIG. 21 illustrates a bypass arrangement for test architectures.

FIG. 22 illustrates example circuitry for enabling the FIG. 21 bypassarrangement.

FIG. 23 illustrates the use of data resynchronization circuits in theserial path between test architectures according to the Disclosure.

FIG. 24 illustrate an example circuit for the FIG. 23 dataresynchronization circuits.

DETAILED DESCRIPTION

The circuits and processes disclosed in this patent are used inmanufacturing to test and ensure proper operation of the integratedcircuit products before sale. The circuits and processes disclosed inthis patent can also be used after the sale of the integrated circuitproducts to test and ensure the continued proper operation of theintegrated circuit products and possibly to develop and test softwareproducts associated with the integrated circuit products.

FIG. 6A illustrates a preferred test architecture 601 for accessing thewrappers 307-308 of FIG. 3, according to the present Disclosure. In thetest architecture 601, wrappers 307-309 have been positioned between aninput linking circuitry 602 block and an output linking circuitry 603block, such that the wrapper serial inputs (SI-1, SI-2, SI-3) are outputfrom the input linking circuitry 602 and the wrapper serial outputs(SO-1, SO-2, SO-3) are input to the output linking circuitry 603. Thewrapper serial outputs (SO-1, SO-2, SO-3) are also input to the inputlinking circuitry 602. The input linking circuitry 602 receives a serialinput SI 604 and the output linking circuitry 603 outputs a serialoutput 605. The control inputs (CTL-1, CTL-2, CTL-3) of wrappers 307-309are commonly connected to test interface CTL bus 109. The input andoutput linking circuitry 602 and 603 receive control inputs from awrapper Link bus 606. The enable inputs (Enable-1,2,3) of wrappers307-309 are provided by an Enable bus 607.

FIGS. 6B and 6C illustrate example implementations of input linkingcircuitry 602 and output linking circuitry 603, respectively. Inputlinking circuitry 602 of FIG. 6B comprises multiplexers 608-610 whichprovide selectable connections between the serial inputs (SI-1, SI-2,SI-3) of wrappers 307-309 and signals SI 604, SO-1, SO-2, and SO-3.Multiplexers 608-610 receive linking control (SELSI-1, SELSI-2, SELSI-3)inputs from Link bus 606. The link control inputs 606 to multiplexer 610enable the SI-3 serial input to wrapper 309 to be connected to SI, SI-1,or SI-2. The link control inputs 606 to multiplexer 609 enable the SI-2serial input to wrapper 308 to be connected to SI, SI-1, or SI-3. Thelink control inputs 606 to multiplexer 608 enable the SI-1 serial inputto wrapper 307 to be connected to SI, SI-2, or SI-3. Output linkingcircuitry 603 of FIG. 6C comprises multiplexer 611 which, in response tolink control inputs from Link bus 606, allows connecting either the SO-1output of wrapper 307, the SO-2 output of wrapper 308, or the SO-3output of wrappers 309 to SO 605.

FIG. 7 illustrates the various wrapper arrangements 7001-7007 possiblebetween the SI 604 and SO 605 of test architecture 601. These wrapperarrangements are formed by inputting link controls to input and outputcircuitry 602 and 603 via Link bus 606, and by inputting enable controlsto wrappers 307-308 via Enable bus 607. Arrangement 7001 contains onlywrapper 307 between SI and SO. Arrangement 7002 contains wrappers 307and 308 in series between SI and SO. Arrangement 7003 contains wrappers307 and 309 in series between SI and SO. Arrangement 7004 containswrappers 307, 308, and 309 in series between SI and SO. Arrangement 7005contains wrapper 308 between SI and SO. Arrangement 7006 containswrappers 308 and 309 in series between SI and SO. Arrangement 7007contains wrapper 309 between SI and SO.

As can be seen in FIG. 7, the test architecture 601 allows for thewrapper arrangement 301 of FIG. 3 as well as many different wrapperarrangements. The Link 606 and Enable 607 inputs to test architecture601 may come from IC pads or from circuitry within the IC, such as anIEEE 1149.1 Test Access Port circuit. While IC pads or Test Access Portcircuits may provide the Link and Enable inputs, a preferred method ofproviding the Link and Enable inputs to the test architecture 601 isdescribed in detail below.

FIG. 8A illustrates circuitry for providing the Link 606 and Enable 607control inputs to test architecture 601, according to the presentDisclosure. The circuitry includes a Link Instruction Register (LIR) 801in series with the test architecture 601. The LIR 801 has a serial input802 connected to SO 605 of the test architecture 601, a serial output(SO) 803, control inputs connected to test interface control bus 109,and control outputs 804 connected to the Link 606 and Enable 607 inputsof test architecture 601. The LIR 801 consists of 3-bit instructionregister (IR) 805, a multiplexer 806, and gating circuitry 807.

During instruction scan operations, the select signal 808 of control bus109 is high to enable the gating circuitry 807 to pass the controlsignals 109 to the 3-bit IR 805 and to connect the serial output of IR805 to SO 803 via multiplexer 806. In the instruction scan mode, the3-bit IR 805 shifts instruction data when the test architecture shiftsinstruction data. Thus, during instruction scan operations, the 3-bit IR805 becomes part of the instruction scan path between SI 604 and SO 803.

During data scan operations, the select signal 808 of control bus 109 islow to disable the gating circuitry 807 from passing control signals 109to the 3-bit IR 805 and to connect SO 605 of test architecture 601 to SO803 via multiplexer 806. In the data scan mode, the 3-bit IR 805 isdisabled and the LIR simply forms a bypass connection between the SO 605of test architecture 601 and the SO 803 of the LIR. Thus, during datascan operations, the LIR is included in the data scan path between SI604 and SO 803, but it does not add to the bit length of the data scanpath. Also, since the control bus 109 is gated off during data scanoperations, the data contained in the LIR's IR 805 cannot be changedduring data scan operations.

It should be noted that while the LIR 801 has been shown inserted in theserial output path from the test architecture 601 (i.e. LIR input 802connected to test architecture SO output 605), it could be have beensimilarly inserted in the serial input path to the test architecture 601as well (i.e. LIR output 803 connected to test architecture SI input604). Thus the position of the LIR 801 with respect to it beingpositioned at the beginning or ending of the serial path through thetest architecture does not impact its ability to provide control of theLink 606 and Enable 607 bus inputs to the test architecture 601.

FIG. 8B illustrates that the circuitry of the 3-bit IR 805 consists of a3-bit shift register 810, a 3-bit update register 811, and decode logic812. During the shift step of an instruction scan operation, the 3-bitshift register 810 shifts data from its serial input to its serialoutput. During the update step of an instruction scan operation the datashifted into the 3-bit shift register 810 is transferred to the 3-bitupdate register 811. The 3-bit update register outputs this data todecode logic 812. The outputs of decode logic 812 respond to the datainput from the 3-bit update register to output Link 606 and Enable 607control signals to test architecture 601 via bus 804. Reset signal 809of control bus 109 is used to initialize shift register 810 and updateregister 811, such that bus 804 may be set to a desired Link and Enableinput state to test architecture 601. While the examples of FIGS. 8A and8B use a 3-bit IR, the IR could be of any bit length. The use of a 3-bitIR will be seen to be sufficient in selecting the wrapper arrangementsdescribed in regard to FIG. 9 below.

FIG. 9 illustrates the various wrapper arrangements 9001-9007 between SI604 and SO 803 in response to different 3-bit codes scanned into LIR801. When the reset signal 809 is activated, the instruction registers105 of wrappers 307-309 are initialized to a first instruction thatselects the bypass registers 106 of the wrappers and enables normaloperation of their associated cores. Also in response to the resetsignal 809, LIR 801 is initialized to contain all zeros, i.e. LIR=000.

As seen in arrangement 9001, when the LIR contains a 000 code followinga reset or an instruction scan operation it outputs Link 606 and Enable607 control to enable and connect wrapper 307 in the scan path betweenSI 604 and SO 803. The other wrappers 308-309 are disabled anddisconnected from the scan path between SI 604 and SO 803.

As seen in arrangement 9002, when the LIR contains a 001 code followingan instruction scan operation it outputs Link 606 and Enable 607 controlto enable and connect wrappers 307 and 308 in the scan path between SI604 and SO 803. Wrapper 309 is disabled and disconnected from the scanpath between SI 604 and SO 803.

As seen in arrangement 9003, when the LIR contains a 010 code followingan instruction scan operation it outputs Link 606 and Enable 607 controlto enable and connect wrappers 307 and 309 in the scan path between SI604 and SO 803. Wrapper 308 is disabled and disconnected from the scanpath between SI 604 and SO 803.

As seen in arrangement 9004, when the LIR contains a 011 code followingan instruction scan operation it outputs Link 606 and Enable 607 controlto enable and connect wrappers 307-309 in the scan path between SI 604and SO 803.

As seen in arrangement 9005, when the LIR contains a 100 code followingan instruction scan operation it outputs Link 606 and Enable 607 controlto enable and connect wrapper 308 in the scan path between SI 604 and SO803. The other wrappers 307 and 309 are disabled and disconnected fromthe scan path between SI 604 and SO 803.

As seen in arrangement 9006, when the LIR contains a 101 code followingan instruction scan operation it outputs Link 606 and Enable 607 controlto enable and connect wrappers 308 and 309 in the scan path between SI604 and SO 803. Wrapper 307 is disabled and disconnected from the scanpath between SI 604 and SO 803.

As seen in arrangement 9007, when the LIR contains a 110 code followingan instruction scan operation it outputs Link 606 and Enable 607 controlto enable and connect wrapper 309 in the scan path between SI 604 and SO803. The other wrappers 307 and 308 are disabled and disconnected fromthe scan path between SI 604 and SO 803.

In all arrangements 9001-9007, instruction scan operations shift datathrough the 3-bit IR 805 of LIR 801, but data scan operations do notshift data through the 3-bit IR 805 of LIR 801, as previously described.A current arrangement 9001-9007 will be maintained following aninstruction scan operation as long as the 3-bit LIR code is not changedby the instruction scan operation.

Some advantages of using the LIR 801 to control the Link 606 and Enable607 inputs to the test architecture 601 are listed below.

The LIR 801 exists and operates within the scan path of each selectedwrapper arrangement 9001-9007. Therefore no additional circuitry and/orinterfaces (for example no 1149.1 Test Access Port and/or IC interfacepads as mentioned in regard to FIG. 7) are required to control the Link606 and Enable 607 buses to switch between wrapper arrangements.

The LIR 801 provides the opportunity of switching between wrapperarrangements 9001-9007 following each instruction scan operation. Thusthe shifting in and updating of LIR wrapper arrangement codes andwrapper test instructions may be performed during the same instructionscan operation.

The LIR 801 does not add bits to a selected wrapper arrangement9001-9007 during data scan operations. By not adding to the bit lengthof a given wrapper arrangement, the test patterns applied to the wrapperarrangement do not have to be modified to accommodate the presence ofthe LIR. For example, if a test pattern set existed for testing core 1using the internal scan register 108 (FIG. 1) of wrapper 307,arrangement 9001 could be selected via an instruction scan operationthen the test patterns could be applied using data scan operations.Since the LIR does not add bits to the length of arrangement 9001 duringdata scan operations, the core 1 test pattern set can be applied withoutmodification, enabling core 1 test pattern reuse

FIG. 10 illustrates an example of a core 4 1001 which has a wrapper1002. Core 4 differs from the previously described cores 1-3 in that itcontains an embedded core A 1003 having a wrapper 1004 and an embeddedcore B 1005 having a wrapper 1006. Access to wrapper 1002 is providedvia SI-4, SO-4, CTL-4, and Enable-4. Access to wrapper 1004 is providedvia SI-A, SO-A, CTL-A, and Enable-A. Access to wrapper 1006 is providedvia SI-B, SO-B, CTL-B, and Enable-B.

FIG. 11 illustrates the test architecture 1101 of the present Disclosurebeing used to provide access to wrappers 1002, 1004, and 1006 of core 4.The test architecture is similar to the test architecture 601 describedin regard to FIG. 6 with the exceptions that; (1) wrapper 1002 has beensubstituted for wrapper 307, (2) wrapper 1004 has been substituted forwrapper 308, (3) and wrapper 1006 has been substituted for wrapper 309.

FIG. 12 illustrates the wrapper arrangements 1201-1207 selectable viathe Link 606 and Enable 607 buses of test architecture 1101. The wrapperarrangements 1201-1207 are the same as wrapper arrangements 7001-7007 ofFIG. 7 with the exceptions that; (1) wrapper 1002 has been substitutedfor wrapper 307, (2) wrapper 1004 has been substituted for wrapper 308,(3) and wrapper 1006 has been substituted for wrapper 309.

FIG. 13 illustrate a test architecture 1301 of the present Disclosurewhich contains wrapper 307, wrapper 308, and the test architecture 1101of FIG. 11. Test architecture 1301 is similar to the test architecture601 of FIG. 6 with the exception that test architecture 1101 has beensubstituted for the core 3 wrapper 309. Test architecture 1301 isserially connected to an N-bit LIR 1302 which provides control input viabus 1303 to the Link 606 and Enable 607 buses of test architecture 1301and to the Link and Enable buses 1306 of test architecture 1101, asdescribed previously in regard to the 3-bit LIR 810 of FIG. 8A. TheN-bit LIR 1302 is similar to the 3-bit LIR 810 except that its IRcontains addition bits for decoding the additional Link and Enable-4, A,B signals 1306 required by test architecture 1101.

Embedding test architecture 1101 within test architecture 1301 requiresthat the Link and Enable-4, A, B signals 1306 of test architecture 1101be brought out of test architecture 1301 so they can be controlled bythe N-bit LIR via bus 1303. Thus the N-bit LIR not only provides theLink 606 and Enable 607 signals for test architecture 1301, but also theLink 606 and Enable signals 1306 for the embedded test architecture1101.

FIG. 14 illustrates in 1410 the N-bit LIR 1302 controlled arrangements1401-1407 of test architecture 1301. As can be seen in 1410, the N-bitLIR can be loaded with codes to select; (1) wrapper 307 between SI 1304and SO 1305 (arrangement 1401), (2) wrappers 307 and 308 between SI andSO (arrangement 1402), (3) wrapper 307 and test architecture 1101between SI and SO (arrangement 1403), (4) wrappers 307, 308, and testarchitecture 1101 between SI and SO (arrangement 1404), (5) wrapper 308between SI and SO (arrangement 1405), (6) wrapper 308 and testarchitecture 1101 between SI and SO (arrangement 1406), and (7) testarchitecture 1101 between SI and SO (arrangement 1407).

FIG. 14 further illustrates in 1420 that when test architecture 1101 isincluded in a test architecture 1301 arrangement between SI 1304 and SO1305, the N-bit LIR provides control for selecting the particulararrangement between the 1101 test architectures SI 1102 and SO 1103. Ascan be seen in 1420, the N-bit LIR can be loaded with codes to select;(1) wrapper 1002 between SI 1102 and SO 1103 (arrangement 1201), (2)wrappers 1002 and 1004 between SI and SO (arrangement 1202), (3) wrapper1002 and 1006 between SI and SO (arrangement 1203), (4) wrappers 1002,1004, and 1006 between SI and SO (arrangement 1204), (5) wrapper 1004between SI and SO (arrangement 1205), (6) wrapper 1004 and 1006 betweenSI and SO (arrangement 1206), and (7) wrapper 1006 between SI and SO(arrangement 1207).

FIGS. 10-14 have illustrated how one test architecture 1101 of thepresent Disclosure may be embedded within another test architecture 1301of the present Disclosure and both test architectures accessed using asingle LIR. For simplification, only one test architecture 1101 wasillustrated as being embedded in test architecture 1301. However, itshould be understood that a plurality of test architectures 1101 can beembedded in test architecture 1301. For example, substituting a secondtest architecture 1101 for wrapper 308 and a third test architecture1101 for wrapper 307 in FIG. 13 would illustrate the embedding of three1101 test architectures within test architecture 1301.

While only a single level of test architecture embedding was shown, i.e.test architecture 1101 embedded within test architecture 1301, it isclear that the multiple levels of test architecture embedding ispossible using the present Disclosure. When multiple levels of testarchitecture embedding is performed, the number of control signals thatmust be output from the LIR increases, as can be understood from theinspection of bus 1303 of FIG. 13. At some point the number of LIRoutput control signals may reach a level that is unacceptable due towire routing concerns within an IC. The following describes an alternateembodiment of the present Disclosure that provides a solution to thisLIR output control signal wire routing problem.

FIG. 15 illustrates an alternate preferred test architecture 1501according to the present Disclosure that combines the core 4 testarchitecture 1101 of FIG. 11 with a LIR 1502. LIR 1502 is similar to LIR801 of FIG. 8A with the exception that gating circuitry 1503 replacesgating circuitry 807. Gating circuitry 1503 provides, in addition to theselect signal from control bus 109, an additional input for a testarchitecture enable (TAENA) signal 1504. The TAENA signal 1504 issimilar to the select signal 808 in that it operates to; (1) enablegating circuitry 1503 to pass control bus signals 109 to the 3-bit IRduring instruction scan operations, or (2) disable gating circuitry 1503from passing control bus signals 109 to the 3-bit IR during instructionscan operations. Thus the only time the 3-bit IR receives control bus109 signals is when TAENA 1504 and select 808 are both set to enablegating circuitry 1503 to pass control bus 109 signals to the 3-bit IR.

FIG. 16 illustrates a test architecture 1601 of the present Disclosurewhich contains wrapper 307, wrapper 308, and the test architecture 1501of FIG. 15. Test architecture 1601 is similar to the test architecture1301 of FIG. 13 with the exception that test architecture 1501 has beensubstituted for test architecture 1101. Test architecture 1601 isserially connected to an N-bit LIR 1602 which provides control input viabus 1603 to the Link 606 and Enable 607 buses of test architecture 1601and the TAENA signal 1504 to test architecture 1501. The N-bit LIR 1602is similar to the N-bit LIR 1302 except that it contains a reducednumber of bits and control signal outputs, since it does not need todecode all the Link and Enable-4, A, B signals that were required by theembedded test architecture 1101 of test architecture 1301. Embeddingtest architecture 1501 within test architecture 1601 only requires thatthe TAENA signal 1504 be brought out of test architecture 1601 so it canbe controlled by the N-bit LIR via bus 1603.

FIG. 17 illustrates in 1710 the N-bit LIR 1602 controlled arrangements1701-1707 of test architecture 1601. As can be seen in 1710, the N-bitLIR can be loaded with codes to select; (1) wrapper 307 between SI 1612and SO 1613 (arrangement 1701), (2) wrappers 307 and 308 between SI andSO (arrangement 1702), (3) wrapper 307 and test architecture 1501between SI and SO (arrangement 1703), (4) wrappers 307, 308, and testarchitecture 1501 between SI and SO (arrangement 1704), (5) wrapper 308between SI and SO (arrangement 1705), (6) wrapper 308 and testarchitecture 1501 between SI and SO (arrangement 1706), and (7) testarchitecture 1501 between SI and SO (arrangement 1707).

FIG. 17 further illustrates in 1720 that when test architecture 1501 isincluded in a test architecture 1601 arrangement between SI 1612 and SO1613 by appropriate setting of the TAENA signal 1504, the 3-bit LIR 1502of test architecture 1501 is included in the arrangement and madeaccessible during instruction scan operations. The 3-bit LIR of testarchitecture 1501 can be scanned to select any particular arrangementbetween the 1501 test architectures SI 1505 and SO 1506. As can be seenin 1720, the 3-bit LIR 1502 can be loaded with codes to select; (1)wrapper 1002 between SI 1505 and SO 1506 (arrangement 1501), (2)wrappers 1002 and 1004 between SI and SO (arrangement 1502), (3) wrapper1002 and 1006 between SI and SO (arrangement 1503), (4) wrappers 1002,1004, and 1006 between SI and SO (arrangement 1504), (5) wrapper 1004between SI and SO (arrangement 1505), (6) wrappers 1004 and 1006 betweenSI and SO (arrangement 1506), and (7) wrapper 1006 between SI and SO(arrangement 1507).

It should be clear from FIG. 17 that when test architecture 1501 isincluded in an arrangement 1710 of test architecture 1601, two LIRs willbe scanned in series during instructions scan operations, LIR 1602 andLIR 1502. Also it should be clear that since LIR 1502 provides withinthe test architecture 1501 all the control signals required to selectthe test architecture 1501 arrangements 1720, via bus 804 of FIG. 15,the wire routing problem mentioned in regard to FIG. 13 is significantlyreduced. The only control signal LIR 1602 needs to provide to includetest architecture 1501 in an arrangement 1710 is the TAENA signal 1504.Once included, the LIR 1502 of test architecture 1501 becomes enabledand can be scanned to provide all the additional signals required forselecting arrangements 1720 within test architecture 1501.

The advantage test architecture 1501 has over test architecture 1101 isthat when test architectures 1501 is embedded within another testarchitecture 1601, only the TAENA 1504 signal of test architecture 1501is required to be brought out of the other test architecture 1601 to beaccessed by a LIR 1602 connected to the other test architecture 1601.This can be compared to test architecture 1301 of FIG. 13 where it wasrequired to bring out the Link & Enable-4, A, B signals of testarchitecture 1101 to be connected to LIR 1302. As described earlier inregard to test architecture 1101 and 1301 of FIG. 13, multiple testarchitectures 1501 could have been shown embedded within testarchitecture 1610, by simply substituting a second and third testarchitecture 1501 for wrappers 308 and 307 respectively.

The process of making the TAENA signal of an embedded test architecture,like 1501, externally available at the I/O boundary of a next higherlevel test architecture, like 1601, forms the basis of a framework thatcan be used to access any hierarchically positioned test architecturewithin an IC. The following provides an example of this hierarchicaltest architecture access framework and the process for selectingembedded test architectures contained therein.

FIG. 18 illustrates a test architecture 1801 containing wrapper 307,wrapper 308, and the test architecture 1610 of FIG. 16. Testarchitecture 1610 is similar to test architecture 1501 in that itcombines a LIR 1602 with test architecture 1601, as test architecture1501 combined the LIR 1502 with test architecture 1101. Testarchitecture 1610 has a TAENA signal 1611, as test architecture 1501 hasa TAENA signal 1504. Test architecture 1610 is associated with a core 5,as test architecture 1501 is associated with a core 4. The LIR 1802 isconnected to the TAENA 1611 signal of test architecture 1601 via bus1803, as LIR 1602 is connected to TAENA 1504 signal of test architecture1601 via bus 1603.

The process steps of accessing test architecture 1101 embedded withintest architecture 1501, which is further embedded within testarchitecture 1610, which is still further embedded within testarchitecture 1810, is as follows. The process steps below are assumed tostart at a point where only wrapper 307 and LIR 1802 of FIG. 18 are inthe serial path between SI 1812 and SO 1813 of FIG. 18, similar toarrangement 9001 shown in FIG. 9.

Step 1 Perform a first instruction scan operation to load LIR 1802 witha code that sets TAENA 1611, via bus 1803, to a state that enables testarchitecture 1610. Following this instruction scan operation, testarchitecture 1610 and LIR 1802 are in the serial path between SI 1812and SO 1813.

Step 2 Perform a second instruction scan operation to load LIR 1802 witha code that maintains TAENA 1611 at a state enabling test architecture1610, and to load LIR 1602 of test architecture 1610 with a code thatsets TAENA 1504 to a state that enables test architecture 1501.Following this instruction scan operation, test architecture 1501, LIR1602, and LIR 1802 are in the serial path between SI 1812 and SO 1813.

Step 3 Perform a third instruction scan operation to load LIR 1802 andLIR 1602 with codes that maintain TAENA 1611 and TAENA 1504 at statesenabling test architectures 1610 and 1501, and to load LIR 1502 of testarchitecture 1501 with a code that selects a desired arrangement1201-1207 of test architecture 1101. Following this instruction scanoperation, the selected arrangement 1201-1207 of test architecture 1101,LIR 1502, LIR 1602, and LIR 1802 are in the serial path between SI 1812and SO 1813.

Step 4 Perform subsequent instruction and/or data scan operations to theselected arrangement 1201-1207 of test architecture 1101 as required toperform a desired test or other operation via the SI 1812 and SO 1813terminals of the test architecture 1810 of FIG. 18. During subsequentinstruction scan operations, the codes loaded into LIRs 1502, 1602, and1802 should maintain access to the currently selected arrangement oftest architecture 1101, unless a new arrangement is needed. Since, aspreviously mentioned in regard to FIG. 8A, data scan operations cannotchange existing LIR codes, the access to test architecture 1101, setupby Steps 1-3 above, is not effected during subsequent data scanoperations.

At some point in accessing embedded test architectures using data scanoperations, the accumulation of the LIR bypass paths, i.e. the directconnection path coupling the LIR input 802 to the LIR output 803 viamultiplexer 806 of FIG. 8A, may become to long for data to propagate ata desired data scan clock rate. In some cases therefore, it may benecessary to add a resynchronization flip-flop in the serial pathbetween test architectures, such that during data scan operations thedata may be re-timed as it passes between serially connected testarchitectures. A logical point to insert such a resynchronizationflip-flop would be in the LIR bypass path described above. Placing itelsewhere would force instruction scan operations to unnecessarily haveto pass through the resynchronization flip-flop.

FIG. 19 illustrates an LIR 1901 containing a resynchronizationregister/flip-flop 1904 in the bypass path of the LIR. LIR 1901 issimply LIR 801 adapted to include flip-flop 1904 in the bypass pathbetween LIR input 802 and LIR output 803 and circuitry 1902 and 1903 toenable the flip flop 1904 to receive control bus 109 input during datascan operations. During data scan operations the select signal will below to select the registered bypass path through multiplexer 806 to SO803. Inverter 1902 inverts the select signal so that during data scanoperations And gating circuit 1903 passes bus 109 to flip flop 1904. Inresponse to the clock signal of bus 109, flip-flop 1904 moves data fromSI 802 to 50803. Use of LIR 1901 with a registered bypass path betweeninput 802 and output 803 eliminates the above-described concern of usingLIRs with direct connection bypass paths between input 802 and output803.

FIG. 20 illustrates a serial configuration 2001 of test architectures2006-2008. The test architectures 2006-2008 are connected in a serialpath between SI 2004 and SO 2005. The serial path includes a LIR 2002that provides the link and enable control bus 2003 to the testarchitectures. Each test architecture and the LIR receive control inputfrom control bus 109. A TAENA 2009 signal is shown being input to theLIR 2002 to indicate that the serial configuration 2001 of testarchitectures 2007-2008 may itself be a test architecture according tothe present Disclosure, being enabled and disabled by TAENA 2009 aspreviously described in regard to FIGS. 15, 16, and 18. If serialconfiguration 2001 is viewed as a test architecture 2001, it could beembedded within another test architecture as test architectures 1501 and1610 were embedded within other test architectures 1610 and 1810,respectively. The following description assumes the serial configuration(or test architecture) 2001 is enabled by TAENA 2009.

During instruction or data scan operations data flows through theselected arrangement of each test architecture 2006-2008 and through theLIR from SI 2004 to SO 2005. If testing or other operation, such asemulation, is to be performed on only one of the test architectures, sayon test architecture 2007, the selected arrangements of other testarchitectures 2006 and 2008 must be serially traversed during theapplication of the test or other operation. The following descriptionillustrates a modification to the test architectures 2006-2008 thatprevents having to traverse arrangements within test architectures thatare not involved in a test or other operation. This modification will bedescribed as it would be applied if test architectures 2006-2008 are ofthe type 601 shown in FIG. 6A. To illustrate that test architectures2006-2008 are of type 601, the SIs and SOs of test architectures2006-2008 are each labeled as SI 604 and SO 605.

In FIG. 21, a group of arrangements 2101-2108 for the modified testarchitectures 601 are shown. In comparing the group of arrangements ofFIG. 21 to that of FIG. 7, it is seen that arrangements 2101-2107 ofFIG. 21 are identical to the arrangements 7001-7007 of FIG. 7.

The difference between the FIGS. 7 and 21 arrangements is that a newwrapper bypass arrangement 2108 has been added in the arrangements ofFIG. 21. This new wrapper bypass arrangement 2108 provides for directlyconnecting the SI 604 input and SO 605 output of modified testarchitectures 601, such that all wrappers 307-309 contained within themodified test architectures 601 may be disabled and disconnected(bypassed) from the serial path between SO 604 and SO 605.

FIG. 22 illustrates how the output linking circuitry 603 of FIG. 6C ismodified to allow for the new wrapper bypass arrangement 2108. Themodification involves replacing the three input multiplexer 611 of FIG.6C with the four input multiplexer 2201 of FIG. 22 and connecting the SI604 input of test architecture 601 to the fourth input of multiplexer2201. In addition to this modification of the output linking circuitry603, bypass codes for each of the test architectures 2006-2008 need tobe added to the LIR 2002 to enable selecting the wrapper bypassarrangement 2108 of FIG. 21 in each of the test architectures 2006-2008.The following description of a bypass code for test architecture 2006 isgiven.

When the LIR 2002 contains a bypass code for test architecture 2006, itwill output control on bus 2003 to input SELSO 2202 control tomultiplexer 2201 to form the wrapper bypass arrangement 2108 between theSI 604 input and SO 605 output of test architecture 2006. Also when LIR2002 contains the bypass code it will disable the wrappers 307-309 oftest architecture 2006 from responding to control bus 109 by settingtheir Enable-1, 2, 3 inputs low via bus 2003. While test architecture2006 is controlled to the wrapper bypass arrangement 2108, data passesdirectly from its SI 604 input to SO 605 output during instruction anddata scan operations occurring in the serial test architectureconfiguration 2001 of FIG. 20.

If test architectures 2006 and 2008 are controlled to the abovedescribed wrapper bypass arrangement 2108 of FIG. 21 while testarchitecture 2007 is controlled to say the 2105 arrangement of FIG. 21,i.e. core 2 wrapper 308 is selected, then testing or other operationscan occur on the wrapper of core 2 in test architecture 2007 withouthaving to traverse wrapper arrangements in the leading 2006 and trailing2008 test architectures of FIG. 20. Thus more efficient serial access isprovided to the wrapper of core 2 of test architecture 2007 using thewrapper bypass arrangements 2108 in test architectures 2006 and 2008.This increase in serial access efficiency would be even more pronouncedif the example of FIG. 20 had shown a multiplicity of serially connectedtest architectures preceding and following the target test architecture2007.

While the modification to include a wrapper bypass arrangement 2108 hasbeen described as it would apply to the type 601 test architecture ofFIG. 6A, it is a general modification that can be applied to any of thetest architectures described herein. For example, test architecture 1301of FIG. 13, test architecture 1501 of FIG. 15, test architecture 1610 ofFIG. 16, and test architecture 1810 of FIG. 18 could all be modified toinclude the wrapper bypass arrangement described above.

In test architectures that contain an embedded LIR, i.e. testarchitectures 1501, 1610, and 1810, the embedded LIR would include theabove described wrapper bypass codes required to select the wrapperbypass arrangement 2108 of the test architecture. Including the wrapperbypass arrangement in all the above-mentioned test architectures wouldserve to improve the serial access efficiency when the testarchitectures are placed into a serial configuration 2001 as shown inFIG. 20.

In test architectures that contain an embedded LIR (i.e. 1501, 1610,1810), it is preferable to use the LIR 1901 of FIG. 19 as opposed to LIR801 of FIG. 8A, since LIR 1901 allows registering the data transfersduring data scan operations. By registering data scan operationtransfers, any number of serially connected test architectures may beplaced in the wrapper bypass arrangement 2108 and operated withouthaving to reduce the data scan clock frequency, as described in regardto FIG. 19. In test architectures that do not contain an embedded LIR(i.e. 601), it may be necessary to insert a data resynchronizationcircuit (DRC) at points along the serial path connecting multiple testarchitectures to maintain a desired scan clock rate through the serialpath when multiple test architectures are placed in the wrapper bypassarrangement 2108.

For example, FIG. 23 illustrates the serial connection 2301 of themultiple test architectures 2006-2008 of FIG. 20 being connectedtogether serially through DRC's 2302-2304. TAENA 2313 is shown simply toindicate that serial configuration 2301, like serial configuration 2001,may be viewed as an embedded test architecture. As seen in FIG. 23, DRC2302 exists between SO 605 of test architecture 2006 and the SI 604 oftest architecture 2007, DRC 2303 exists between SO 605 of testarchitecture 2007 and SI 604 of test architecture 2008, and DRC 2304exists between SO 605 of test architecture 2008 and the SI 802 of LIR2305. The DRCs 2302-2304 are connected to the clock 2306 signal ofcontrol bus 109, to allow them to operate during both instruction anddata scan operations. The DRCs 2302-2304 are also connected to bypassselect signals 2307-2309, respectively, from LIR output control bus2312. The bypass select signals are signals added to the LIR outputcontrol bus 2312 when DRCs are used. There is one unique bypass selectsignal 2307-2308 for each DRC 2302-2304 to allow separate control ofeach DRC.

FIG. 24 illustrates an example DRC circuit. The DRC contains a flip-flop(FF) 2403 and a multiplexer 2402. The DRC has a SI 2404 that is input tothe multiplexer and FF. The output of the FF is input to themultiplexer. The multiplexer has a control input 2407 and a SO 2405. TheFF has a clock input 2406. The control inputs 2407 of DRC 2302-2304 ofFIG. 24 are connected to the bypass select signals 2307-2309respectively. The clock inputs 2406 of DRCs 2302-2304 of FIG. 24 areconnected to control bus 109 clock signal 2306. The SIs 2404 of DRCs2302-2304 of FIG. 24 are connected to the SOs 605 of test architectures2006-2007 respectively. The SOs 2405 of DRCs 2302-2304 of FIG. 24 areconnected to the SI 604 of test architecture 2007, the SI 604 of testarchitecture 2008, and SI 802 of LIR 2305 respectively.

If LIR 2305 is loaded with a bypass code for test architecture 2006, thebypass select signal 2307 will be set cause DRC 2302 to place FF 2406between the SO output of test architecture 2006 and SI input of testarchitecture 2007. For all other codes, bypass select will be set tocause DRC 2302 to directly connect the SO output of test architecture2006 to the SI input of test architecture 2007 via multiplexer 2402.

If LIR 2305 is loaded with a bypass code for test architecture 2007, thebypass select signal 2308 will be set cause DRC 2303 to place a FF 2406between the SO output of test architecture 2007 and SI input of testarchitecture 2008. For all other codes, bypass select will be set tocause DRC 2303 to directly connect the SO output of test architecture2007 to the SI input of test architecture 2008 via multiplexer 2402.

If LIR 2305 is loaded with a bypass code for test architecture 2008, thebypass select signal 2309 will be set cause DRC 2304 to place a FF 2406between the SO output of test architecture 2008 and SI input of LIR2305. For all other codes, bypass select will be set to cause DRC 2304to directly connect the SO output of test architecture 2008 to the SIinput of LIR 2305 via multiplexer 2402.

As can be seen from the above description of FIGS. 23 and 24, when atest architecture is placed in the wrapper bypass arrangement, the DRCassociated with the SO output of the test architecture is set to insertFF 2406 between its SI 2404 and SO 2405. During instruction and datascan operations, this inserted FF 2406 registers the data output fromthe test architecture in the wrapper bypass arrangement to the SI inputof the next serially connected test architecture.

Also as can be seen from the above description of FIGS. 23 and 24, whena test architecture is not placed in the wrapper bypass arrangement, theDRC associated with the SO output of the test architecture is set toform a direct path between its SI 2404 and SO 2405. During instructionand data scan operations, this direct path simply passes the data fromthe SO output of the leading test architecture to the SI input of thetrailing test architecture. Directly connecting the SO output of a testarchitecture not in the wrapper bypass arrangement is fine since allother selectable arrangement will include registration in the form ofone of the data registers 106-108 described in regard to FIG. 1.

While insertion of DRC FFs 2406 and/or LIR FFs 1904 in the serial pathof series connected test architectures, such as FIG. 23, takes away fromthe test pattern reuse advantage 3 stated earlier in regard to FIGS. 8and 9, it offers the advantage of being able to operate seriallyconnected test architectures at high clock frequencies. Thus while testpatterns may need to be modified when FF 2406/1904 bit positions areinserted in the path between serially connected test architectures, theinserted bit positions facilitate high speed clocking of the datathrough serially connected test architectures.

While DRCs in FIGS. 23 and 24 have been described as they would be usedto register or pass serial test/emulation data between test architecturecircuits 2007-2008, it should be understood that the DRCs could also beused to register or pass functional data between functional circuits aswell. For example, circuits 2006-2007 could represent functionalcircuits in an IC or on a board, such as microprocessors, digital signalprocessors, memories, mixed signal circuits (A/D, D/A), or any othertype of circuits that are connectable via their inputs and outputs tocommunicate data. Using DRCs, the data communicated between functionalcircuits could selectively be communicated in either a registered ornon-registered form, as described above in regard to FIGS. 23 and 24.

Although the present Disclosure has been described in accordance to theembodiments shown in the figures, one of ordinary skill in the art willrecognize there could be variations to these embodiments and thosevariations should be within the spirit and scope of the presentDisclosure. Accordingly, modifications may be made by one ordinarilyskilled in the art without departing from the spirit and scope of theappended claims.

What is claimed is:
 1. A test architecture within an integrated circuitcomprising: A. a plurality of core wrappers each having a serial input,a serial output, and control inputs, the control inputs including aclock input, a shift input, a capture input, an update input, a resetinput, an enable input, and a core select input; B. input circuitryhaving a serial input, a plurality of serial outputs, each selectivelycoupled to the serial input, and control inputs, each serial outputbeing connected to the serial input of a core wrapper; C. outputcircuitry having a plurality of serial inputs, a serial output, and acontrol input, each serial input being connected to the serial output ofa core wrapper and each serial input being selectively coupled to theserial output; and D. a link instruction register having a serial input,a serial output, control inputs, and control outputs, i. the controlinputs including a clock input coupled to the clock input of the corewrappers, a shift input coupled to the shift input of the core wrappers,a capture input coupled to the capture input of the core wrappers, anupdate input coupled to the update input of the core wrappers, and alink select input coupled to the select input of the core wrappers, ii.the control outputs including plural enable outputs, each enable outputbeing coupled to the enable input of a core wrapper, and the controloutputs including select outputs coupled to the control inputs of theinput circuitry and the output circuitry, iii. the serial input and theserial output of the link instruction register being connected in serieswith the serial input of the input circuitry and the serial output ofthe output circuitry, and iv. the link instruction register including aninstruction register connected to the serial input and to the controloutputs, and a multiplexer connected to the serial input, the serialoutput, and the select input.
 2. The test architecture of claim 1 inwhich the integrated circuit is formed on a semiconductor substrate. 3.The test architecture of claim 1 in which the instruction registerincludes a shift register selectively connected in series between theserial input and the serial output of the link instruction register. 4.The test architecture of claim 1 in which the instruction registerincludes a shift register, an update register, and decode logic.
 5. Thetest architecture of claim 1 in which the link instruction registerincludes a logic gate selectively controlling at least some of thecontrol inputs in response to a select signal on the select input. 6.The test architecture of claim 1 in which the link instruction registerincludes a logic gate selectively controlling the control inputs, exceptfor a reset signal on a reset input, in response to a select signal onthe select input.
 7. The test architecture of claim 1 in which theinstruction register has a serial input connected to the serial input ofthe link instruction register and a serial output selectively connectedto the serial output of the link instruction register by themultiplexer.